Coating of an interior surface of a cylinder, such as a pipe or tube, may be accomplished, for example, by pouring a coating composition and rotating the cylinder. However, the resulting coating may have a significant variance in the thickness of the resulting thin film of the coating composition.
Spray coating the interior of a cylinder may be accomplished by an air atomizing or airless spray nozzle mounted on a lance that is reciprocated into and out of the cylinder while the cylinder is rotated. Various issues associated with spray coating may include uneven film thickness, helical streaks or runs along the cylinder wall, such as may be due to a low viscosity for the coating material), and slumping, as may result when the coating solution is too thick. Overspray and the maintenance issues associated with overspray should also be considered with respect to costs and maintenance.
Spray coating may be performed, for instance, using a bore centralizer to control or maintain the position of the spray nozzle or the lance at the center of the cylinder. For example, a spray nozzle may be provided with multiple spring-loaded legs to maintain the nozzle in the center of the cylinder. The length of the legs may be such that the centralizer may be used for cylinders having different internal diameters.
Use of a bore centralizer may be potentially satisfactory for a single cylinder internal diameter. However, such may not be suitable for use with different diameters, as significant issues may be encountered with respect to volume of delivery, atomization/dispersion of the coating material, differences in overspray turbulence, and control of the overlap of the resulting spray per cylinder rotation, among other challenges that may result due to differences in the distance between the internal surface of the cylinder and the spray nozzle. Control issues may also be exacerbated by a cylinder having an irregular internal surface, including maintenance of the spray nozzle in the center of the bore.